When a feeding tube is inserted through a patient's nostril, there is always some chance that the end will be misdirected into his lungs instead of his stomach. Unfortunately, the patients at highest risk of having this occur are those who are critically ill such that their cough and gag reflexes are inhibited.
Various pleuropulmonary complications can arise as a result of a misplaced feeding tube, common of which are pneumonia, abscess and empyema. In some instances, no complications arise but in others, they are fatal.
With large bore enteric feeding tubes, it is possible to aspirate some of the stomach contents to confirm proper placement. The pH of the aspirated fluid is a useful indication of proper placement because gastric fluid has a low pH whereas fluid aspirated from other portions of the body, such as the pleural space or lung, has a pH much higher than that of gastric fluid. In general, gastric placement can be differentiated from respiratory placement by testing the pH of the aspirate. Gastric aspirates will be acidic (pH less than 6) as compared to tracheobronchial secretions and pleural fluid which will be alkaline (pH 7 or greater). The pH of the aspirate can be determined with a pH meter or with a pH indicator such as litmus.
With modern, small-bore, polyurethane enteric feeding tubes, however, it is not possible to aspirate fluid through the tubes because the tubes, which were designed for patient comfort and ease of insertion, collapse when sucked on. At the present time, other than for radiography, the proper placement of smallbore feeding tubes is checked by blowing air down the feeding tube and listening for bubbling in the stomach. This test is not entirely reliable even in the hands an experienced operator.
Modern small-bore feeding tubes have a plurality of spaced apart radiopaque markings or a line along the entire length which is visible under x-ray. The use of radiography provides positive evidence of proper placement in the stomach but is expensive and requires that the patient (sometimes critically ill) be transferred to a radiology department. This is particularly a hardship when the patient is in a nursing home and must be transported by ambulance for the x-ray. In the face of these difficulties, it not surprising that the proper placement of the feeding tube is frequently not verified. The incidence of misplacement in the tracheobronchial tree is unknown but anecdotal reports suggest that intrapulmonary placement of feeding tubes is an under-reported occurrence.